1. Field of the Disclosure
This application relates generally to the surface mount of electronic components onto a printed circuit board by employing a reflow process, and more particularly to a compression box of a reflow soldering oven that is designed to provide uniform airflow of heated air to the printed circuit board during the reflow process.
2. Discussion of Related Art
In the fabrication of printed circuit boards, electronic components are often surface mounted to a bare board by a process known as “reflow soldering.” In a typical reflow soldering process, a pattern of solder paste is deposited onto the circuit board, and the leads of one or more electronic component are inserted into the deposited solder paste. The circuit board is then passed through an oven where the solder paste is reflowed (i.e., heated to a melt or reflow temperature) in the heated zones and then cooled in a cooling zone to electrically and mechanically connect the leads of the electronic component to the circuit board. The term “circuit board” or “printed circuit board,” as used herein, includes any type of substrate assembly of electronic components, including, for example, wafer substrates.
For each heating zone, reflow ovens incorporate a series of compression boxes, which serve the purpose of distributing heated convection air to a printed circuit board during the reflow soldering process. The reflow soldering process has recently advanced by transitioning from traditional tin-lead solder to lead-free materials. These new soldering materials have reduced the process windows and require that the temperature variances across a printed circuit board be reduced. The importance of reduced temperature variance, known in the industry as “ΔT,” has driven the need to optimize the design of the compression box for uniform airflow to achieve uniform heating of the printed circuit board across its entire width.
Large temperature variances across a printed circuit board can result in insufficient heating of solder joints or overheating of printed circuit board components. These defects can result in rework and/or scrap of the printed circuit board, which can be extremely costly to the printed circuit board manufacturer.